Influence of hydrodynamic parameters on transfer of Disinfection By-Products in ambient air of indoor

swimming pool: use of Residence Time Distribution approaches on a reference basin

Philippe Humeau*, Nicolas Garandel**, Julien Guilhot*, Monem

Masri Idlibi*, Nicolas Cimetière** * Centre Scientifique et Technique du Bâtiment, AQUASIM, 11 rue Henri Picherit, BP82341, 44323 Nantes Cedex 3, France

** Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Av. du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France

2

Context

Health impact of the presence of trichloramine in the air surround the pools

Airborne concentrations above 0.5 mg.m-3

Duration of exposure

Trichloramine concentrations in the air

Renewal of ambient air

Potential of trichloramine emission by the water of the swimming pool

Water concentration

Agitation by swimmers…

Recommendations to limit the presence of Disinfection by-products in water

Larger adding water in the swimming pool

Implementation of dechloramination processes on the recirculating water loop

3

Analyse of emission processes

nAz = NAz × a × S × dz

NAz = KG × (H.CLi – CG

iE)

Specific surface area (m-1)

Presence of swimmers Surface agitation

+

Swimming pool surface (m2)

Specificity of the volatil DBP

Water temperature Air temperature

+

- Air renewal

Overall transfer coefficient in gas phase (m.s-1)

Bustle due to toboggan, backwash, bubbles…

+

DBP concentration in water

Attendance Precursor concentrations Chlorine concentration

+

- Dechloramination processes Water renewal Volume of the pool? Recirculation rate of water?

It is necessary to set specific operating conditions on the issue of NCl3 in the ambiant air

4

Methodological approach

Formation kinetics of disinfection by-

products

Degradation kinetics of disinfection by-

products

Hydrodynamic behaviorof the referenceswimming pool

Hydrodynamic behaviorof air on the reference

swimming pool

Liquid/Gas transferkinetics

Disinfection of swimming pool

Liquid/Gas transfer

Estimate of emission potential of disinfection by-products in ambient air of pool reference

Sanitary objectives:- Regulatory threshold- Sanitary risks

Indoor air quality

Analysis of chlorinatedby-products in air and

water phases

Legend

Literature data: text in italicsExperimental data :

Chemical engineering approaches

5

Presentation of the hydrodynamic study

Experimental hydrodynamic study

Hydrodynamic characterization of a reference swimming pool

3 water recirculation rates: 15 m3.h-1 ; 25 m3.h-1 ; 40 m3.h-1

3 air velocities: 0 m.s-1 ; 2 m.s-1 ; 8 m.s-1

Numerical study of water flow (CFD methods)

Hydrodynamic characterization of a reference swimming pool: validation of calculation methods

Modelisation of hydrodynamic behavior with ideal reactors

Extrapolation ability of the method to a real pool

Location of the flow characteristics (dead volumes, short-circuits…)

6

Material and methods: the swimming pool

Reference swimming pool

Possibility to install a dechloramination device

Possibility to inject a tracer

Characteristic Value

Useful volume Lenght Width Water height Number of injections Water recirculation rate Air velocity Water treatment Water temperature management

42,24 m3 8 m 4 m

1.32 m 4

15 m3.h-1 to 40 m3.h-1

2 m.s-1 0.2 m.s-1 to 8 m.s-1 0.4 m.s-1

Filtration with sand filter, chlorine disinfection, pH regulation

Option

7

Residence Time Distribution (RTD)

The liquid flow has been represented by a tanks-in-series with or without mass exchange model (DTS Pro 4.20 software – Progepi, Nancy)

Q

V.JuaT 1

1

2

V

VK

Q.

Vt 2

m

J

V2

V1

Q Q

Q

Pulse-injection of a non transferable tracer (lithium chloride) at the inlet of the swimming pool

RTD curve obtained by recording the concentration-time of tracer leaving the swimming pool

Residence Time Distribution curve

Numerical study of water flow (CFD method)

The swimming pool is discretized with a Hexahedral mesh type, and includes about

900 000 cells

Turbulence Model: RNG k-ε • Cμ = 0.0845 • C1ε = 1.42 • C2ε = 1.68

Two-phase Model: • DPM (Discrete Particule Motion) • Turbulent dispersion taken into

account • Passive tracer

Material: water • Density: ρ = 998.2 kg/m3

• Viscosity : μ = 0.001003 kg/m.s

Schemes : • Pressure and velocity are coupled with the

SIMPLE scheme • Spatial resolution : Upwind First order method

Boundary conditions: • uniform velocity with a 5%

turbulent intensity at the inputs • Free pressure outlet conditions • 5 mm roughness for the walls of

the pool • smooth walls for the rest (gutter,

pipe, and the water surface)

Simulations Fluent 14.5

Reference : Cloteaux et al. (2013), Influence of swimming pool design on hydraulic behavior: a numerical and experimental study, Engineering, Vol. 5, pp. 511-524

Numerical study of water flow (CFD method)

Hydrodynamic behavior of the water phase

RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1, and 3 different air velocities (0, 2 and 8 m.s-1)

0

0,5

1

1,5

2

2,5

0 20 40 60 80 100 120

Série1

Série2

Série3

Uair = 0 m.s-1

Time (minutes)

Lith

ium

co

nce

ntr

atio

n

(mg.

L-1)

Uair = 2 m.s-1

Uair = 8 m.s-1

The air flow seems to have a significant influence over the pool on the hydrodynamic behavior of the water phase in the pool

Experimental Residence Time Distribution

RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 0 m.s-1)

Deconvolution method on the experimental RTD curves with a compartment model (tanks-in-series) developed by INRS (France)

RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 8 m.s-1)

Mean Residence Time t = 1 h 13 min Mean Residence Time t = 1 h 10 min

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

E (

)

Uair = 0 m.s-1

Uair = 8 m.s-1

Experimental Residence Time Distribution

RTD curves of water in the swimming pool for a water flow rate of 40 m3.h-1 with 2 air velocities (Uair = 0 and 8 m.s-1)

The air velocity has no significant effect on hydrodynamic behavior of the water phase in the swimming pool

Air velocity

Space time

Mean residence time

/ Observation

0 m.s-1

8 m.s-1

1 h 03 min

1 h 03 min

1 h 13 min

1 h 10 min

1.1617

1.1193

Short-circuit

Short-circuit

CFD: Velocity magnitude

Visualizations of water flow in the pool

Water flow rate = 40 m3.h-1

Uair = 0 m.s-1 (not taken into account)

Numerical Residence Time Distribution

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

E (

)

Experimental RTD

Numerical RTD

RTD curve of water in the swimming pool for a water flow rate of 40 m3.h-1 (Uair = 0 m.s-1)

Comparison of experimental and numerical RTD curves of water in the swimming pool for a water

flow rate of 40 m3.h-1 (Uair = 0 m.s-1)

The experimental Residence Time Distribution is correctly represented by the numerical Residence Time Distribution

Numerical mean residence time t = 1 h 07 min

The hydrodynamic parameters (as the mean residence time) are well-estimated by numerical approaches

Influence of operating conditions on

hydrodynamic behavior of the water

0

0,002

0,004

0,006

0,008

0,01

0,012

0,014

0,016

0 3600 7200 10800 14400 18000 21600 25200 28800 32400 36000

Trac

er p

rop

ort

ion

at

the

ou

tlet

of

the

po

ol

Time(s)

inj1

inj2

inj3

inj4

total

0

0,002

0,004

0,006

0,008

0,01

0,012

0,014

0,016

0 3600 7200 10800 14400 18000 21600 25200 28800 32400 36000

Tra

cer

pro

po

rtio

n a

t th

e o

utl

et

of

the

po

ol

Time(s)

inj1

inj2

inj3

inj4

total

RTD curve of water in the swimming pool for a water flow rate of 15 m3.h-1 (Uair = 0 m.s-1)

RTD curve of water in the swimming pool for a water flow rate of 25 m3.h-1 (Uair = 0 m.s-1)

Water flow rate

Space time

Mean residence time

/ Observation

15 m3.h-1

25 m3.h-1

40 m3.h-1

2 h 49 min

1 h 42 min

1 h 03 min

3 h 32 min

1 h 59 min

1 h 07 min

1.2544

1.1647

1.070

Short-circuit

Short-circuit

Short-circuit

Disrupting flows of water (short-circuits) increase with the reduction of water flow recirculation rate in the swimming pool

Modeling of the hydrodynamic

behavior of the swimming pool

Réacteur Q (m3.h-1) Volume (m3)

J Tm K Pe

1 0,4 0,0875 - - - 0,5

2 0,4 0,875 - - - 0,5

3 0,4 1 - - - 1

4 0,4 1 - - - 1

5 3,35 0,2333 - - - 1

6 3,35 0,2333 - - - 1

7 3,35 0,4258 - - - 1

8 3,35 0,4258 - - - 1

9 3,35 19,679 1 10 0,2048 -

10 3,35 19,679 1 10 0,2048 -

11 3,35 38,574 1 10 0,2048 -

12 3,35 38,574 1 10 0,2048 -

Hydrodynamic parameters of the flow model of the liquid phase in the reference basin (Q = 15 m3.h-1, Uair = 2 m.s-1)

Determination of the influence of operating conditions and pool water features on liquid/gas transfer performance of Disinfection By-Products

Sensitivity analysis of the transfer model according to the hydrodynamic parameters

Perspectives

17

Liquid/Gas transfer modelisation

References : Humeau et al. (2004), Optimization of bioscrubber performances: experimental and modeling approaches, J. Environ. Eng.-ASCE, Vol. 130 n°3, pp. 314-321

Prediction model of the emission of disinfection by-products in the air atmosphere of the reference basin

Gerardin et al. (2014), Modeling of variations in nitrogen trichloride concentration over time in swimming pool water , Process Safety and Environmental Protection , 11 p. http://dx.doi.org/10.1016/j.psep.2014.10.004

V 1

V 2

Q

V 1

V 2

Q

V 1

V 2

Q

V 1

V 2

Q

1 n n + 1 J

Fresh air Polluted Air

Water recirculation

18

Liquid/Gas transfer: equations

J

Z.pxe1.CC.'HCC i

GiL

1iG

iG

1iG

iG

iL

1iL CC.CC

Gas :

Liquid :

Partial mass balance equations, for an elementary volume of compartment i :

:

:

The resolution of the mass balance equations is obtained using an iterative method

Plug flow

Plug flow with dispersion

Transfer without reaction

Transfer with reaction

(dissociation model)

G

G

Q

S.a.K

2G

aG

a

G

U

D.a.K.411.

D.2

U

1

23

21

3

2

L

G

OH

K.K

OH

K1.

Q.

S.a.K

L

G

Q.

S.a.K

Conclusion

19

Characterization of the hydrodynamic behavior of the water in the reference basin

Impact of operating conditions on hydrodynamic parameters

Experimental Residence Time Distribution

Numerical Residence Time Distribution Validation of the method by comparison with experimental data obtained on the reference basin

Modeling the hydrodynamic behavior of a real pool according to its geometry and operating conditions

Prediction of Liquid/Gas transfer of Disinfection By-Products Relevant method for the estimation of the impact of operating conditions on the potential of adverse gaseous emissions and the measurement of the performance of the water treatment devices

Thank you for your attention